In recent years, in order to enhance performances of various safety devices, for example, airbags and seatbelts that are provided at a vehicle, operations of these safety devices may be controlled according to a weight of an occupant seated in a seat. For example, when the occupant is seated in the seat without wearing the seatbelt, a warning lamp warns that “seatbelt is unbuckled” after seating is detected. Further, the law stipulates that the airbag is to be deployed at a vehicle collision when an adult is seated in a passenger seat. The law further stipulates that a deployment of the airbag should be prohibited in a case where a child safety seat is fixed to the passenger seat facing backward so that an infant or a child in the child safety seat and a driver can see each other because an impact by the deployment of the airbag causes adverse effects to the infant or the child. In these cases, a weight of a smaller female adult is applied as a criterion for determining whether an occupant is an adult, and a criterion for determination on the child safety seat is also stipulated. Thus, in order to ensure safety, it is important that a load of, for example, the occupant in the seat is detected and that a state in the seat is determined correctly.
An example of a known occupant detection apparatus is disclosed in JPH9-207638A (which will be hereinafter referred to as Patent reference 1), which distinguishes whether or not an occupant is in a seat by detecting a load acting on the seat. According to the known occupant detection apparatus disclosed in Patent reference 1, a load sensor is provided at each of two seat attaching portions among plural seat attaching portions. It is distinguished whether or not the occupant is in the seat on the basis of a sum of two load values that are obtained from the respective load sensors. Thus, according to Patent reference 1, the known occupant detection apparatus includes the load sensors arranged at the only two minimum necessary seat attaching positions from among usual four positions, and therefore the occupant detection apparatus which has a simple configuration and is inexpensive as a whole is provided.
An example of a known seating determination apparatus is disclosed in JP2011-16396A (which will be hereinafter referred to as Patent reference 2), which detects a load acting on a seat to determine whether or not a child safety seat is attached to the seat. According to the known seating determination apparatus disclosed in the Patent reference 2, a load sensor is provided at each of two seat attaching portions at left and right sides (especially, the two portions at left and right sides of a rear portion) among plural seat attaching portions. It is distinguished whether or not a child safety seat is attached to the seat by detecting load fluctuations characteristically generated while the child safety seat is being fastened to the seat on the basis of a sum of two load values and a difference between the two load values. Thus, according to Patent reference 2, the known seating determination apparatus includes the load sensors arranged at the only two minimum necessary positions at the left and right sides, and therefore the seating determination apparatus which has a simple configuration and is inexpensive is provided.
According to each of the above-described known apparatuses of Patent reference 1 and Patent reference 2, in order to reduce costs and weight of the apparatus, the number of the load sensors provided is two and the occupant is distinguished with the two load sensors. However, according to the above-described manner in which the load sensors are attached to the two seat attaching positions among plural seat attaching portions, load values detected by the load sensors may fluctuate toward a negative side. Specifically, in a case, for example, where a vehicle is stopped on an inclined location such as a slope way so that a front-rear direction of the vehicle and an inclination direction make a large angle therebetween and where the load sensors are at that time positioned higher on the inclination relative to the seat, a load which is given by a seat body to the load sensors is reduced. At this time, in a case where an adult is seated on a seating surface of the seat, the buttocks of the adult slide downwardly along the inclination of the seating surface, and thus the center of gravity of the adult moves downwardly. As a result, the detected load of the load sensors further fluctuate toward the negative side. On the other hand, in a case where a child safety seat is fastened to the seat, a large fluctuation of the center of gravity of the child safety seat is not generated by the inclination of the vehicle. Thus, the load which is given by the child safety seat and by the seat body to the load sensors is decreased only slightly corresponding to an amount of the inclination of the vehicle. Accordingly, a difference between the load which is outputted by the load sensors when the adult is seated in the seat and which largely fluctuates toward the negative side, and the load which is outputted by the load sensors when the child safety seat is attached to the seat and which slightly fluctuates toward the negative side is smaller than an actual difference. Consequently, it is difficult to distinguish the adult seated in the seat and the child safety seat attached to the seat.
A need thus exists for a seat occupancy determination apparatus which is not susceptible to the drawback mentioned above.